1. Field of the Invention
The present invention relates to tanks with floating roof. More particularly, the present invention relates to sump drainage apparatus whereby a series of pivotally connected pipes allow liquids that are accumulated on the top surface of the floating roof to be drained. Additionally, the present invention relates to sump drainage systems whereby the floating roof can drop to a bottommost position within the tank without interference from the sump drainage system.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Floating roof tanks are tanks that have no fixed roof. On these floating roof tanks, any water that collects on the roof, through precipitation falling on the roof, should not be drained into the product stored into the tank. Therefore, drainage systems for floating roofs generally include some type of drain line, such as a pipe or a hose, fluidly connecting a drain point on the floating roof to a drain point outside the tank. The drain line will pass through a wall of the tank. In such systems, the water from the roof usually enters the drain line via a sump located at the center of the floating roof, then drains through the line and exits the tank through a valve located near the bottom of the tank wall.
Floating roof drainage systems have heretofore been of two basic designs. The first design includes a hose drain. In this design, a hose is connected to a sump on the floating roof, runs through the product and then is attached to a penetration in the tank wall just upstream of the drain valve. The hose must be weighted because it is normally dry and self-buoyant. Such hoses are generally made of reinforced rubber-like materials, and are subject to mechanical and chemical abuse from the operation of the tank and/or from the product stored in the tank.
A second design has included pipes interconnected by swing joints. The concept of the second design is to provide a conduit which is much more resistant to mechanical and/or chemical abuse than are the hoses in the first design. However, the swing joint design also has weaknesses. Most importantly, the alignment of such pipes will create a structure within the interior of the tank that can interfere with the movement of the floating roof. As the floating roof drops due to the release of liquids from the interior of the tank, it will eventually encounter obstructions caused by this interconnected pipe system. Since the sump extends downwardly from the bottom surface of the roof for a small distance, the sump will create a obstruction with the underlying piping system and, hence, prevent the floating roof from dropping to its lowest possible point. The dropping of the roof to a low position is important so as to allow for the maximum use of the tank. If it is not possible to withdraw a maximum amount of liquid or fluid from the interior of the tank, then the tank will be at less than its maximum capacity and optimum utilization. As such, it is desirable to allow the floating roof to drop to as low as possible during the descent of the roof caused by the withdraw of liquids and/or fluid from the interior of the tank.
In the past, various patents have issued relating to such drainage systems for sumps of a floating roof tank. For example, U.S. Pat. No. 2,643,023, issued on Jun. 23, 1953 to F. D. Moyer, describes a unique type of sump wherein a structure is placed at the top of the roof so as to drain liquid from the sump. A flexible pipe extends above the floating roof so as to allow the liquid to be drained with a downward movement of the floating roof.
U.S. Pat. No. 2,717,095 issued on Sep. 6, 1955 to M. W. Gable, describes another type of drainage apparatus for a movable roof. This apparatus includes a pair of pipes hingedly connected together. A hose extends along these pipes. One of the pipes is pivotally connected to an underside of the roof. The other pipe is pivotally connected to the floor. Each of the pipes is located directly below the sump of the movable roof. As such, the device tends to block the descent of the roof to its lowest possible position.
U.S. Pat. No. 3,154,214, issued on Oct. 27, 1964 to C. E. Baker, discloses a roof drain for a floating roof tank. A conduit has components that are hingedly connected together. A hose extends along a first pipe which is hingedly connected to a second pipe. Additionally, the hose extends along the second pipe and a third pipe which are hingedly connected together in an accordion fashion. The accordion arrangement of pipes appears to be located below the sump and not offset therefrom. As such, when the roof is in its lowermost position, the structure of the pipes will tend to prevent the roof from descending to its lowest level.
U.S. Pat. No. 4,034,887, issued on Jul. 12, 1977 to W. R. Sherlock, teaches a storage tank with a floating roof and a drainage system. The drainage system includes a flexible conduit extending between the roof and a drain pipe adjacent the base of the tank. The lower end of the conduit is sealed relative to the drain pipe. There is a connection between the upper end of the conduit and the upper surface of the roof so that rainwater accumulating on the roof can pass down the conduit to the drain pipe. This pipe extends along the side of the floating roof.
U.S. Pat. No. 4,214,671, issued on Jul. 29, 1980 to McKibbin et al., discloses a another floating roof drainage system that includes a plurality of pipes. The pipes are connected to each other to form a completely welded system and are suspended from the bottom of the floating roof. The pipes will pivot with respect to one another so as to move as the roof moves.
U.S. Pat. No. 4,248,357, issued on Feb. 3, 1981 to D. C. Stafford, provides another type of drain that includes a flexible coiled hose having a lower outlet end in communication with a conduit inlet in a lower portion of the tank. The drain has an upper inlet end in communication with a sump space on the floating roof deck. The coiled hose is extensible in length for a distance at least equal to the height that the floating roof is vertically displaceable in the tank whether it is full or empty of liquid.
FIG. 1 generally illustrates the problems associated with the prior art piping system for use with the sump 10 of a floating roof 12. As can be seen, a first pipe 14 is hingedly connected at pivot 16 to a second pipe 20. An outlet pipe 22 is hingedly connected to an opposite end of the second pipe 20 from the pivot 16 with the first pipe 14. The outlet pipe 22 will extends so as to emerge outwardly of the wall 24 of the tank 26. It can be seen that when the sump 10 reaches its lowermost position, the structure of the outlet pipe 22 and/or the hinge connection 28 between the outlet pipe 22 and the second pipe 20 will block the downward movement of the floating roof 12 to its lower position. As such, it is not possible to drain any liquids in the tank 26 that would reside below the bottom surface of the floating roof 12 and the top surface of the bottom 30 of tank 26. It is an object of the present invention to provide a drainage system for the sump of a floating roof tank which allows the floating roof to drop to its lowermost position within the tank without obstruction.
It is another object of the present invention to provide a drainage apparatus for use with a sump of the floating roof tank that is of a configuration that can be easily introduced through the manhole of the tank.
It is a further object of the present invention to provide a drainage apparatus for use with a sump of a floating roof tank which is easy to install, easy to use and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.